The overall objective of this proposal is to allow the principal investigator to describe the growth and development of the infant lung in health and disease. This is pursuant to a long term career goal of studying infant lung disease, its risk factors and sequelae in order to define and assess strategies of prevention and treatment. As such the project is divided into two phases: The first will be the development of the safe, efficient, and noninvasive techniques needed to study infantile pulmonary function and the development of airways reactivity. Specific assessment of methods of standardization, sources of variability and techniques of digital analysis will be emphasized during this phase. To accomplish this the investigator proposes to study techniques including the measurement of forced expiratory flow, forced oscillatory resistance, tidal flow-volume loop analysis, quasi-static and dynamic pulmonary compliance, inductive plethysmography and airway challenge with cold air and ultrasonically nebulized, distilled water. The second phase will lead to the development of normative data and a prospective description of the changes in pulmonary physiology during infancy. This will also include the assessment of a group of infants at high risk for hyper-reactive airways to determine whether or not such reactivity can be detected prior to the onset of viral respiratory infection. The investigator will also make use of techniques in digital data acquisition and analysis in order to maintain a high level of efficiency and accuracy. The successful completion of this project will thus give the investigator the expertise and methodologies necessary to continue a research career assessing acute and chronic pulmonary disorders during infancy with specific reference to their risk factors, natural history, sequelae, prevention and treatment.